This invention pertains to demountable cams or eccentrics, and more particularly to demountable cams of varying throw lengths which can be easily interchanged to alter the length of the stroke of the needle bar in a tufting machine, including an adjusting means for maintaining the position of the bottom of the stroke.
In some manufacturing applications, it is desirable to be able to vary the stroke of connecting rods, which are imparted with longitudinal motion by the shape of an eccentric on a rotating shaft or axis. It is particularly desirable to be able to change the length of the needle stroke of tufting machines, and to be able to make such a change without the necessity for removing the entire driveshaft of the machine. In tufting machines, one or more rows of yarn carrying needles are reciprocally driven through a backing material fed through the machine across a bed plate to form loops that are seized by loopers oscillating below the backing material and bed plate in timed relationship with the needles. To change the depth of pile height produced by a tufting machine, it is necessary to change the length of the stroke of the needle, and the elevation of the bed plate relative to the loopers, as is well known in the art and described in U.S. Pat. No. 2,977,905. The actual bottom point of the stroke of the needle must remain constant so that the loopers and needles retain their proper relationship. Otherwise, the loopers will not properly seize the loops of yarn from the needles. To maintain this relationship a variety of methods have been utilized including interchanging push rods, or connecting rods of varying lengths; using shims; or using adjustable length push rods or connecting rods. In order to properly maintain the relationship between the needles and loopers, changes to the length of the needle stroke as well as the attendant adjustments are generally performed with the tufting machine at bottom dead center of the needle stroke.
Changing the stroke in high speed tufting machines has previously been accomplished by two general constructions. In one construction, the eccentrics are adjustable. The most widely used adjustable eccentrics involve two non-adjustable hubs which can be clamped tightly against the eccentric. When the hubs are loosened, the eccentric can be adjusted to alter its throw. Other types of adjustable eccentrics have generally either involved too many parts and adjustments to make changes in stroke length quickly and correctly, or have lacked the structural stability required to withstand the radial forces of driving the connecting rod and needle assembly at high speeds. Examples of such adjustable eccentrics are illustrated in U.S. Pat. Nos. 3,857,345 and 4,515,096. In the other general type of construction, two eccentrics of different throws are mounted on the rotating shaft adjacent to each connecting rod. To adjust the stroke, the eccentric strap is loosened and the eccentric with the desired throw is engaged. This leaves unused eccentrics mounted on the rotating shaft.
In tufting machines using either type of construction, there are a considerable number of eccentrics on each machine because there is an eccentric for each push rod, and there may be from 8 to 12 push rods in a full size tufting machine. Each time a stroke adjustment must be made, it is necessary to make adjustments at each push rod internal of the tufting machine head, and the head of the machine must be opened and substantially disassembled for changes to be performed. Because of the expense due to the number of parts involved, as well as the machine down-time involved in adjusting the eccentrics, these mechanisms are generally only used for specialized or high speed machines. In tufting machines that operate at higher speeds, it is desirable to reduce the vibration and rotating mass of the drive mechanism.
In the constructions utilizing adjustable eccentrics a great deal of undesirable weight is added to the drive shaft by the two hubs which support the eccentric. This is aggravated by the need to add different balancing weights depending upon the setting of the eccentric to minimize the vibration attendant to high speed rotation. The weight on the drive shaft may be further increased by the addition of "dummy" push rods that operate in opposite reciprocation with the actual push rods so that the force necessary to power the machine remains fairly constant, with resulting smoother operation. The aggregate weight places tremendous stress upon the main driveshaft with a corresponding reduced useful life for the shaft or the need to use a stronger and more expensive shaft.
A substantial amount of undesirable weight also is added to the drive shaft in the constructions using a plurality of cams for each push rod, because the unused cams remain on the driveshaft. In addition, as only two cams can reasonably be placed on the driveshaft for each push rod, the possible adjustments are limited to only two throw lengths.